[SR-Users] How to reply an INVITE with 403

Hi All, I want to handle a special case in the Kamailio 4.1.3. When I receive INVITE from some UAC I wanto reply it with 403 message. I am using the Kamailio in Proxy mode when the INVITE comes I want to reply it with 403 and do not want to send this INVITE to SIP Server. I expored the Kamailio source code and found that fucntion receive_msg() in file receive.c receives all the SIP messages. I am able to parse the SIP INVITE from such UACs but how to reply them with 403 SIP Code. I am unable to use the t_reply("403","Forbidden") here in this function/file. Also in this function finally the forward_reply(msg); is called which sends the INVITE to the Sip Server. But I dont want to send anything to SIP Server in this case but want to reply the UAC with 403. Can you please guide me how to do and where to do this. I am new to kamailio. Please help. Regards Varun